This research has two long-term objectives: (1) to provide new information that will improve our understanding of segmental spinal reflexes and (ii) to determine how suitable spinal nocifensive reflexes in animals are as models of pain perception in humans. The studies of organization of reflex mechanisms will focus on two issues. The first is the way in which reflexes recorded simultaneously from synergistic muscles may be influenced differently by inputs from higher levels of the nervous system. Work currently under way focuses on a description of these differential influences of motor neuron pools subserving the reflex response of different muscles. Future work will try to uncover the mechanisms responsible for the differences observed Such studies may provide important information not only about the organization of motor systems, but may also yield new knowledge that can improve clinical strategies for patients with motor disorders. The studies of nocifensive reflexes as models of pain perception have more potential clinical application than do those of organization of spinal reflexes. Investigation of both the basic mechanisms and new clinical management of pain rely heavily on the use of such reflexes. However, there have been few efforts to determine just how reliable the reflexes are as models of pain. The studies outlined here are designed to physical data from studies using human subjects. Two specific goals will be pursued in the first year. The first is to determine if prolonged central summation of the flexion and crossed extension reflexes in decerebrate cats is produced by the same mechanisms that contribute to summation of nociception in humans. The second is to determine if the flexion and crossed extension reflexes in spinal cats are sufficiently different than those in decerebrate cats to make them better or worse models of pain perception.